In wireless communication, a technology of controlling the emission direction of a transmission wave emitted form an antenna has been developed. Such a technology is referred to as beam forming. In the beam forming, transmission waves the phases of which are different from one another are emitted from the respective ones of a plurality of antennas. A plurality of transmission waves emitted from the plurality of antennas strengthen one another by having the same phase in a specific direction and weaken one another by having the reverse phases to cancel one another in another direction. Using the above phenomenon, the beam forming is capable of performing control of emitting transmission waves concentrated on any desired direction or emitting no transmission wave in any desired direction.
In the description of the present invention, the beam forming will be described mainly from the standpoint of transmitting carrier waves. However, from the standpoint of receiving transmission waves, the beam forming is also capable of performing control of receiving a transmission wave transmitted from any desired direction in a strengthening manner and not receiving any transmission wave transmitted from another direction.
In the above-described beam forming, it is required to appropriately select a phase of a transmission wave transmitted from each antenna and to control the state thereof. In order to control a phase, using a transmitter including a phase shifter is conceivable.
FIG. 6 is a functional block diagram exemplifying a known transmitter including the phase shifter 101. Transmitters 100a and 100b illustrated in FIG. 6 make phase shifters 101 shift the phases of respective transmission waves generated by a signal source 109, and, via power amplifiers 107, supply antennas 103 with the phase-shifted transmission waves. The antennas 103 transmit the transmission waves amplified by the power amplifiers 107. Phase shift amounts in the phase shifters 101 are determined in accordance with phase control signals output from not-illustrated control circuits.
Switching the emission directions of transmission waves dynamically using the transmitters 100a and 100b described above requires the phases of the transmission waves supplied to the respective antennas to be selected with high accuracy. A phase shifter that dynamically switches the phase of a transmission wave is described in, for example, NPL 1.
In PTL 1, detecting a phase error amount between a transmission branch and another transmission branch is disclosed. According to PTL 1, the detected phase error amount takes a maximum value when a phase difference between the transmission branch and the another transmission branch indicates the same phase and a minimum value when the phase difference indicates reverse phases. A transmission device disclosed in PTL 1, using such a phenomenon, controls the phase difference between a transmission branch and another transmission branch to the same phase or reverse phases.